The perfect off-break has drift and dip. The idea is to deceive the batsman into thinking that the ball will pitch closer to him than it will and secondly to separate his bat from his pad.
Cricket is a sideways-on game. To bowl a perfect off-break it is necessary to be very sideways-on. The tendency is to look at the batsman beneath the left arm; on the contrary you must look at him over the left shoulder. The length of the run up is immaterial. Bob Appleyard used to bowl off-breaks from a run-up as long as Freddie Trueman's: Jim Laker took only a few paces. You hold the ball across the seam and apply clockwise rotation to it at the time of delivery. The ball has to be given some air. These flat-jack off-spinners are just trying to bore the batsman out. The rotation of the body in delivery, the high arm necessitated by the over-the-shoulder presentation and the rotation of the ball will provide the drift and dip.
The batsman will see it as a half-volley and be drawn into the drive, the the dip means that he doesn't get to the pitch of it. He will think he has got the line right but the drift will deceive him. As the ball drifts to the off he has already planted his front foot and can't move that so he follows the ball with his bat, opening the gate between bat and pad. Then as the ball pitches it breaks back and takes the off peg.
I bowled my last perfect off-break eleven years ago next September. The memory lingers.